As is known in the art, there has been an increase in the number of countries which control and have access to missiles and missile technology such as cruise missiles and the technology associated therewith. Consequently, systems to detect, track and intercept such missiles have become of increasing importance.
One approach used to defend against cruise and other types of missiles involves deployment of existing Surface-to-Air Missile (SAM) systems. One problem with this approach, however, is that the number of SAM systems required to provide protection is related to the amount of area which must be covered as determined by the horizon limit of ground based sensors. Consequently, a relatively large number SAM systems must be deployed to provide an adequate defense. Thus, it is relatively expensive and in some cases cost prohibitive to use this approach.
Another problem with the ground based sensor approach is that it is relatively difficult for ground based sensors to detect missiles and other objects traveling at low altitudes. Furthermore, the topography of the terrain (e.g. mountains, etc . . . ) surrounding the geographic location of the ground based sensor can mask portions of the horizon from the ground based sensor. Since incoming cruise missiles typically travel at relatively low altitudes, it is difficult for ground based sensors to provide early warning of incoming cruise missiles.
Yet another approach to defend against missile attacks is referred to as air directed surface-to-air missile (ADSAM) defense. In this approach, sensors elevated on stationary platforms at a height generally in the range of about 15,000 to 20,000 feet detect cruise or other missiles. The elevated platforms are typically provided as inflatables which are tied to the ground via a tether. One such type of inflatable is referred to as an aerostat. A sensor is typically coupled to the airship via a structure which rotates in the azimuth plane to thus provide sensor coverage over a wide area in the azimuth plane.
The so elevated sensor detects and tracks targets and in some cases attempts to perform some early classification to identify potential cruise or other missiles. The sensor transmits data to a ground based theater tactical operation center (TOC) which assigns an aerostat based precision track and illuminate radar to track the missile. The sensor performs precision track on potential cruise missiles and also performs additional classification, discrimination and identification (CDI) tasks.
This precision track data is relayed from the aerostat sensor to a surface-to-air missile (SAM) system which includes a missile system radar. In response to a SAM system missile launch, uplink data is supplied to the missile by the missile system radar. The sensor target track data continues to be supplied to the missile system until the missile intercepts the target.
If the missile includes an on board transmitter (i.e. the missile includes an active seeker system) the missile will then obtain independently radar lock on the incoming cruise missile and home on it. If the missile does not include an on board transmitter (i.e. the missile includes a passive seeker system) then the missile is provided terminal illumination by the sensor and the missile detects portions of the sensor signal reflected off the target to home in on the target. Although this approach is relatively inexpensive compared with the SAM system approach, conventional sensor systems used in existing aerostats do not have the required sensitivity to detect cruise missiles at long range.
To provide an aerostat based sensor with the sensitivity to detect cruise missiles at long range, the sensor must have an antenna capable of long range detection. To provide such an antenna using conventional antenna systems would require the sensor to include three or four separate active array antenna apertures. Each of such antenna apertures would require their own set of transmit/receive (TR) modules. In addition, with conventional TR module spacing, many TR modules would be required to fill the antenna aperture. For example, a conventional antenna having an aperture of approximately 4 square meters (m.sup.2) would require over 10,000 TR modules. Such an antenna would have electronic scan capability in both azimuth and elevation planes of approximately .+-.53.degree.. The size and weight of such an antenna system makes deployment of such a system in an aerostat or other inflatable relatively difficult since the size, weight and power consumption requirements of such a system are incompatible with the limited ability of present technology aerostats.
It would, therefore, be desirable to provide a radar system which can perform a precision track and illumination function and which has size, weight and power consumption characteristics which allow deployment of the system in an aerostat or other elevated platform.